The energy needs of the stressed patient appear to be optimally provided when fat is incorporated into the parenteral regimen. However conventional long chain triglyceride emulsions are less well tolerated by severely injured patients. Recently interest has been generated in the use of triglyceride emulsions containing only medium chain fatty acid or structured with long chain fatty acids. Potential benefits of medium chain triglycerides as calorie sources in hospitalized patients include their preferential oxidation and their limited ability to undergo elongation or deposition. However, although controlled trials in injured laboratory animals have demonstrated improved hepatic and reticuloendothelial function with triglyceride emulsions containing medium chain fatty acids exclusively, no benefit for protein metabolism over currently used long chain triglyceride emulsions has been identified. On the other hand when burned rats receive total parental nutrition containing medium chain and long chain fatty acids that were chemically synthesized into a structured triglyceride, weight gain, protein retention (nitrogen balance), isotope balance, liver protein synthesis, and serum albumin were markedly improved. The long range goals of the present study are to define the metabolic and physiologic differences that might explain these profound effects on protein metabolism including 1) mechanism of lipid absorption from the gut and lipid uptake by muscle cells 2) determine the optimal dose of structured lipid to achieve these effects 3) confirm the putative benefits of structured lipid in one other conventional injury model (septic fracture) and one novel injury model (burn injury + monokine infusion) and 4) investigate whether the function of the reticuloendothelial system is relatively preserved with parenteral administration. These studies will be the design model for subsequent human investigation if the early promise of structured lipid is confirmed.